1. Field of the Invention
The invention relates to oscillating inductors which are of wide distribution in electrical engineering.
2. Description of the Background Art
Nowadays, traditional standard kits from the E-core RM-range are preferably used in electronic ballasts for starting and operating fluorescent tubes, such as those described on pages 61-01 to 61-06 in the VOGT electronic AG “Inductive Component” catalogue from the year 2000.
The increase in voltage in order to start fluorescent lamps is achieved by means of a series resonant circuit formed from an LC combination. This is described, for example, on pages 60-04 and 60-05 in the already mentioned VOGT electronic AG catalogue. In this case, voltages of up to 4 kVpp are produced across the coils, and currents of up to 3.5 A, or more, have to be handled.
As a result of the required performance, these operating conditions for the starting coil or oscillating coil lead to air gaps up to a maximum of 8 mm, depending on the kit. Air gaps of this order of magnitude lead to high eddy current losses in the copper windings, caused by the stray field from the core. The low AL value (permeability times the form factor) caused by the large air gap necessitates a relatively large number of turns, and this necessarily leads to high copper losses (Pv=I2·R). The high eddy current losses also mean that it is essential to use braids for oscillating inductors such as these. These braided structures have a number of disadvantages in comparison to solid wires. Their supply is more expensive, their temperature properties and their mechanical properties are not as good as those of normal varnished copper wires, braids are more difficult to wind than normal varnished copper wires and, finally, braids result in difficulties when fitting the wires to pins, owing to the unraveling effect.
In order to reduce the eddy current losses, some coils are nowadays cushioned, that is to say the distance between the winding and the core is artificially increased by introducing insulating films, or by injection of thick walls, into the coil former in the area of the air gap. This measure in turn necessarily leads to the overall component having a larger volume and to the available winding spaces being smaller.